Microorganism growth is driven by many factors, so it is critical to be able to assess the quality of blood samples quickly and accurately. Without this ability, samples might need to be discarded or, alternatively, result in or worsen illnesses. Although bacterial blood contamination is rare, it does occur and has led to deaths. A rapid screening method could mean that a larger percentage of blood could be directly tested for bacteria.
Jie Shao, associate professor at the Institute of Information Optics at Zhejiang Normal University, explains that microorganism growth is always associated with the production of carbon dioxide (CO2), so assessing CO2 levels within, for example, closed compartments like bottles or bags would allow them to detect this growth quickly.
Several detection techniques are currently capable of rapid and accurate measurements of gas compositions. Those based on optical spectroscopy are most appealing because they're noninvasive, boast high sensitivity, provide instant responses, and are potentially useful for assessment of bacterial growth. So, the researchers developed an instrument based on a technique called tunable diode laser absorption spectroscopy (TDLAS), which combines all of these properties with ease of use and low cost, Shao says. What's more, it can achieve low detection limits on the order of parts per billion, and measure temperature, pressure, velocity, and mass flux.
The research team used their instrument—which includes a tunable diode laser as the light source, beam shaping optics, a sample to be investigated, receiving optics, and one or more detectors—to assess bacterial growth of various types of samples under a variety of conditions. By applying the technique to transparent containers of organic substances such as food items or medical samples, bacterial growth can be quickly evaluated.
In contrast with conventional and more invasive techniques that require contact with the tested items, the TDLAS method is truly noninvasive for monitoring—in real time—the status of food and medical supplies, or as a tool to determine under which environmental conditions bacterial growth is expected to be severe.
Next, the researchers plan to enhance the technique to allow for assessments of microbial growth in a large variety of samples, expanding beyond food items and medical supplies, Shao says.
Full details of the work appear in the journal Applied Optics.